Brake rotor for a motor vehicle

ABSTRACT

A brake rotor includes a disc-shaped carrier and friction rings arranged on or on top of the carrier, so that the friction rings and carrier form a single piece construction. The carrier and friction rings are made from carbon/carbon materials and ceramic materials respectively. The carrier has a hat-shaped cross-sectional shape with a flanged outer edge and the friction rings are attached to each side of the flanged edge of the carrier. The brake rotor may be directly mounted onto the wheel flange via the carrier using bolts.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/049,451, filed Jun. 12, 1997.

This invention relates to a brake rotor constructed from a hat-shapedcarrier and at least one friction ring located on or on top of thecarrier.

Similar brake rotors are known as components of braking systems,especially for use in motor vehicles. Known brake rotors are made ofcast gray iron and comprise a hat-shaped carrier section and a frictionring arranged at the circumference of the carrier section.

Known cast gray iron brake rotors have a coefficient of thermalexpansion of 10⁻⁵ K⁻¹. They exhibit, at increased temperatures resultingfrom the application of the brake pads, a radial expansion and also anaxial expansion due to the connection of the friction ring with thehat-shaped carrier section (commonly known as umbrella distortion). Tominimize undesirable umbrella distortion, known brake rotors employgrooves to block heat transfer.

It is known that to accomplish higher temperature capability, frictionrings used in motor sport applications are constructed of carbon/carbonand/or ceramic materials. Drilled holes increase the ventilation of thebrake rotor.

The attachment of the friction ring to the hat-shaped brake rotorrequires a variety of fastener hardware such as bolts, spacer bushings,nuts, washers etc. This attachment of the friction ring to the brakerotor transmits torque and accommodates the thermal expansion of thedifferent component materials. Because of new carbon/carbon and ceramicfriction materials, the brake rotor and fastener components mustwithstand higher temperatures. The disadvantages of attaching thefriction ring to the brake rotor in this manner include a high partnumber count, the additional assembly work required, and the potentiallynegative effect on comfort. Required manufacturing tolerances regardingparallelism, thickness and runout have a negative effect regardingcomfort even with the known cast gray iron brake rotors.

One object of this invention is to provide a brake rotor which overcomesthe disadvantages of brake rotors manufactured per the current state oftechnology as described above. Another object is to provide a brakerotor that is easy to manufacture and install. In addition, an object isto provide a brake rotor able to operate at higher temperatures withoutexposing nearby components of the wheel, especially the wheel bearingand rim, to higher temperatures. Moreover, another object of the brakerotor is low cost and preferably low weight.

These and other objects are obtained by the present invention. The brakerotor of the present invention includes a friction ring made of a highperformance friction material from the group of fiber reinforced ceramicmaterials, and a carrier made of a material from the group ofcarbon/carbon materials; the coefficients of thermal expansion for thesematerials are at least approximately the same; and the friction ring andcarrier are immovably attached to each other. By using the same- orsimilar materials having a low thermal expansion, the occurrence of thepreviously described umbrella distortion is eliminated. In addition,because of the low thermal conductivity of the carrier material, only asmall portion of the heat generated by the braking process is conductedto the wheel bearing and rim of the wheel being braked.

The brake rotor of the present invention is easier to manufacture andassemble than known brake rotors from motor sport, which use a floatingassembly, because there are fewer parts to handle. Additionally, thebrake rotor of the present invention provides improvements in comfortbecause tolerance buildup, experienced with known brake rotors due tothe assembly of the friction ring to the brake rotor, does not occurwith the present invention.

A particularly advantageous configuration of the brake rotor of thepresent invention is the arrangement of friction rings on both sides ofthe flanged outside diameter portion of the hat-shaped carrier.

The brake rotor further includes attachment of the friction ring(s) tothe carrier by riveting, bonding or a homogeneous material joint.

The brake rotor includes a carrier configuration with recesses on itsflange portion for ventilation which cover the radial dimensions of thefriction rings attached on both sides and provides cooling to thefriction rings. Recesses serve as cooling channels and do not requiresubsequent drilling or elaborate assembly of brake rotor halves to formcooling channels, as required with known brake rotor configurations. Therecesses are readily produced as an integral step in the manufacturingprocess.

Another aspect of the invention is that the hat-shaped carrier containsa flanged bottom in the center of the part to facilitate a boltedattachment to the wheel flange. Attachment to the wheel flange withbolts is preferred to further reduce the number of required parts forassembly.

The objects of the present invention may be obtained by employing amanufacturing process characterized such that the carrier and thefriction ring are molded separately into pre-forms. They aresubsequently joined together and finish-formed in a press tool.Accordingly, the carrier and friction rings are separately pre-formed ina molding press and subsequently assembled and finish molded into asingle part. The process is proven, very efficient, and highly accurate.

This method of manufacture is especially advantageous where anadditional process after the molding process is employed to convert themolded part into carbon/carbon material. Through this process thematerial transition joint present after molding between friction ringsand carrier is eliminated. The result is a seamless materialtransition--the brake rotor becomes, in effect, a single piece part.This leads to especially homogeneous thermal conductivity as well asvery good stability of the brake rotor.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a brake rotor for a firstembodiment according to the present invention;

FIG. 2a is a schematic cross-sectional view of a brake rotor for asecond embodiment taken along section line II--II of FIG. 2b;

FIG. 2b is a schematic top view of a brake rotor for a second embodimentaccording to the invention;

FIG. 3a is a schematic cross-sectional view of a brake rotor for a thirdembodiment taken along section line III--III of FIG. 3b;

FIG. 3b is a schematic top view of a brake rotor for a third embodimentaccording to the invention;

FIG. 4 is a schematic top view of a brake rotor for a fourth embodimentaccording to the invention; and

FIG. 5 is a schematic cross-sectional view of a known, current state ofthe art brake rotor, e.g., used in motor sport applications (forclarity, only the upper portion of the rotationally symmetrical brakerotor is shown).

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 5 shows schematically a known brake rotor. The brake rotor assembly110 includes a hat-shaped brake rotor 112 and a friction ring 114mounted on the circumference of brake rotor 112. Friction ring 114 isattached to brake rotor 112 by spacer bushing 116, where hex head bolt118 passes through and extends beyond spacer bushing 116, and washer 120is placed over the extended end of hex head bolt 118 and hex head nut122 is fastened to the end of hex head bolt 118. The key feature of theattachment is that spacer bushing 116 is engaged with matching slots 113in brake rotor 112 prior to insertion of spacer bushing 116 into themounting holes 115 in friction ring 114.

In FIG. 5, the known brake rotor assembly 110 is a carbon/carbon brakerotor used, for example, in motor sports. Friction ring 114 is made froma carbon/carbon material and hat-shaped brake rotor 112 is made from ametallic material. Friction ring 114 is fastened to brake rotor 112 asdescribed above. Cooling channels to facilitate ventilating the interiorof the friction ring of the known brake rotor have to be machined byseparately drilling each hole. The run out accuracy suffers because thebrake rotor assembly 110 is assembled by attaching two parts (hat-shapedbrake rotor 112 and friction ring 114). An elaborate assembly technique,as described, is necessary to prevent destruction of the friction ringdue to different coefficients of thermal expansion for friction ring 114and hat-shaped brake rotor 112.

Referring to FIG. 1, a first embodiment of the brake rotor of thepresent invention is shown. The brake rotor 10 comprises carrier 12 andfriction rings 14 located on either side of carrier 12. Carrier 12 isessentially a disc with the cross sectional shape of a top hat or a potwith a flanged outer edge 16. The friction rings 14 are located oneither side of flanged outer edge 16 and immovably attached to carrier12. Carrier 12 is attached to wheel flange 18, by bushings 20 in thebolt holes, whereby reinforcement of the bolt holes can be accomplishedusing metallic bushings 20.

According to the invention, carrier 12 and friction rings 14 are madefrom high performance friction materials such as carbon/carbon orceramics. The carrier material is preferably of a laminated structure toachieve especially good mechanical properties for torque transmission.The friction ring material is preferably "chopped" friction material.The material for carrier 12 and the material for friction rings 14 aremolded to the desired pre-form in the "green" state (not fully cured),utilizing press tools, and parts are subsequently joined and finishmolded in a combination mold tool. Processing to fully cure and convertthe molded part to carbon/carbon follows. This process results in anespecially sound and rigid transition bond between the materialsutilized materials for carrier 12 and friction rings 14, producing a"single piece" configuration of brake rotor 10. The final finishfabrication involves standard turning and grinding operations.

FIG. 1 also shows, in broken lines, the brake pads 22 located on eitherside of friction rings 14 and are separated therefrom by a small air gap4. Brake actuation occurs in the known fashion by pressing brake pads 22onto friction rings 14.

The first embodiment of the invented brake rotor shown in FIG. 1 depictsa solid brake rotor without any cooling holes or channels. FIG. 2a andFIG. 2b show a second embodiment of the invented brake rotor 30. FIG. 2bshows a top view of brake rotor 30, and FIG. 2a shows a cross section ofbrake rotor 30 taken along section line II--II.

According to the invention, brake rotor 30 includes a carrier 32 with ahat-shaped cross-section (See FIG. 2a). The disc portion of carrier 32has a central opening 36 used to mount brake rotor 30 onto a wheelflange (not shown). Five bolt holes 38 required to attach carrier 32 tothe wheel flange, are symmetrically arranged surrounding the centralopening 36.

Friction rings 34 are attached to each side of flanged edge 40 ofcarrier 32 forming a "single piece" construction with carrier 32 asexplained above. Friction rings 34 show several attachment pins 42which, in the depicted embodiment, are positioned radially andsymmetrically. As shown in the cross-sectional view of FIG. 2a, thefriction rings 34, extend beyond the edge 40 of carrier 32 and createthe cavities 44 in between, which contribute to cooling the brake rotor.

A third embodiment of the invented brake rotor is shown in FIG. 3a andFIG. 3b. FIG. 3b shows a top view of the invented brake rotor 50 andFIG. 3a shows a cross section of brake rotor 50 taken along section lineIII--III of FIG. 3b.

According to the invention, brake rotor 50 includes a carrier 52 whichshows, as mentioned above, a hat-shaped cross section with flanged edge60. Flanged edge 60 as shown in FIG. 3a and FIG. 3b does not have thecontinuous outside diameter edge as was shown in the examples of FIG. 2aand FIG. 2b. As shown in the top view of FIG. 3b, recesses 62 give theflanged edge 60 a star-like appearance.

Friction rings 54 are, as explained above, immovably attached on eitherside of the flanged edges 60 so as to span the recesses 62, thus forminga "single piece" part with carrier 52. Cavities are formed in the regionof the recesses 62 and between the opposing friction rings 54 whichfacilitate cooling. In addition, friction rings 54 show attachment pins64 similar to those attachment pins 42 shown in the embodiment of FIG.2.

FIG. 4 is a top view of an additional, fourth embodiment of the inventedbrake rotor. Brake rotor 70 is similar to the above described embodimentand includes a carrier 72. Friction rings 74 are attached to either sideof the flanged edge 80 of carrier 72. As depicted in the embodiment ofFIG. 3a and FIG. 3b, brake rotor 70 also employs recesses 82 in theflanged edge 80, forming smaller but more numerous elongated, narrowcut-outs compared to recesses 62 of the example shown in FIG. 3a andFIG. 3b.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

We claim:
 1. A brake rotor substantially eliminating umbrelladistortion, comprising:at least one friction ring comprising a frictionmaterial selected from fiber reinforced ceramic materials, and ahat-shaped carrier comprising a carbon/carbon material, wherein thecoefficient of thermal expansion of the carbon/carbon material of thecarrier is substantially the same as the coefficient of thermalexpansion of the friction material of the at least one friction ring,wherein the carbon/carbon material and the friction material aredifferent materials, wherein the hat-shaped carrier and the at least onefriction ring are immovably attached to each other, and wherein umbrelladistortion during operation is substantially eliminated.
 2. The brakerotor of claim 1, wherein the hat-shaped carrier has a flanged edge,andfurther wherein two friction rings are provided, one each beingattached to different sides of the flanged edge.
 3. The brake rotor ofclaim 2, further comprising rivets which immovably attach the frictionrings to the hat-shaped carrier.
 4. The brake rotor of claim 2, furthercomprising a locked material bond which immovably attaches the frictionrings to the hat-shaped carrier.
 5. The brake rotor of claim 2, whereinthe hat-shaped carrier has at least one recess formed, in an area of theflanged edge, the at least one recess reaching across a radial dimensionof the two friction rings, whereby the friction rings are ventilated. 6.The brake rotor of claim 5, wherein the hat-shaped carrier has a centralopening formed therein and an attachment flange formed therein, theattachment flange adjacent to the central opening, whereby the brakerotor may be attached to a wheel flange.
 7. The brake rotor of claim 2,wherein the hat-shaped carrier has a central opening formed therein andan attachment flange formed therein, the attachment flange adjacent tothe central opening, whereby the brake rotor may be attached to a wheelflange.
 8. The brake rotor of claim 1, further comprising rivets whichimmovably attach the friction ring to the hat-shaped carrier.
 9. Thebrake rotor of claim 1, further comprising a locked material bond whichimmovably attaches the at least one friction ring to the hat-shapedcarrier.
 10. The brake rotor of claim 1, wherein the hat-shaped carrierhas a central opening formed therein and an attachment flange formedtherein, the attachment flange adjacent to the central opening, wherebythe brake rotor is attachable to a wheel flange.